A Resonator Fiber-Optic Gyro (RFOG) has potential to provide the highest possible rotation sensing performance within the smallest possible volume. An RFOG senses rotation by measuring the frequency splitting of resonance frequencies of a fiber ring resonator. To measure the resonance frequencies, the RFOG employs frequency or phase modulation of the laser light used to probe the ring resonator. The resonance detection modulation of the laser frequency or phase produces a signal at the resonator output that is demodulated by a phase sensitive demodulator.
Imperfections in the resonance detection modulation, such as intensity modulation and harmonic distortion, can lead to a large error signal that is approximately 90 degrees (in quadrature) to the primary resonator output signal that is being demodulated. A component of the quadrature error can leak into the in-phase demodulator channel used for detecting resonances if the reference phase of the demodulator is not exactly 90 degrees from the quadrature signal phase. Typically, the large quadrature error is common between the CW and CCW directions of the ring resonator, and therefore subtract out if the phase offsets between the CW and CCW in-phase demodulators and the common quadrature error signal are the same. However, there is always some small difference between the CW and CCW relative reference phase offsets, and thus some quadrature error gets into the rotation measurement. Furthermore, the phase difference between the CW and CCW quadrature errors can drift with temperature or other environmental influences, thus leading to an error in rotation measurement.
One method of controlling the demodulator resonance phase currently used is by introducing a disturbance signal, then controlling the reference phase to zero out a response to the disturbance signal. However, testing has shown a significant drawback to this technique in that the introduction of a disturbance signal typically introduces other unacceptable side effects.